Evaluation of formaldehyde as an ocular irritant: a systematic review and Meta-analysis

The aim of this study was to use meta-regression to evaluate the safety of the maximum allowable dose of formaldehyde in terms of eye irritation symptoms.

We performed a systematic review of literature published in the PubMed, Embase, Lilacs, Web of Science, and Cochrane Library databases. We selected clinical trials, cohort studies, and case-control studies that compared eye irritation between patients exposed and not exposed to formaldehyde. Eighteen of the 2561 studies retrieved met the inclusion criteria. Data were extracted using structured forms and study quality was analyzed using the STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) checklist. Odds ratios (ORs) were calculated using a random effects model with stratification by airborne dose and subsequent meta-regression analysis.

The random effects model yielded an OR of 8.11 (95% CI: 5.85-10.37), with an I2 statistic of 99.8% and p < 0.00001. In the meta-regression analysis, we observed an I2 of 87.29% with an R2 of 23.96; the regression line for exposure had a slope of 1.466 (95% CI: 0.096-2.836) in relation to the Napierian log of the OR. Considering a safety level based on an OR of 2 relative to the unexposed group, an airborne concentration of formaldehyde of less than 0.001 mg/m3 can be considered safe.

Although current formaldehyde exposure concentrations are relatively safe in terms of cancer risk, they continue to cause eye irritation.